The present invention relates to a heating apparatus utilizing an induction heating, particularly, to a fixing apparatus used in, for example, an electrophotographic copying apparatus or a printer apparatus using a toner as a visualizing agent so as to fix the toner image.
In a fixing apparatus incorporated in a copying apparatus using an electrophotographic process, a developing agent image, i.e., a toner image, formed on a transferred material is melted by heating so as to permit the toner image to be fixed to the transferred material. Various methods of heating the toner, which can be employed in a fixing apparatus, have been put to a practical use including, for example, a method utilizing a radiation heat radiated from a halogen lamp (filament lamp), a flash heating method utilizing a flash lamp as the heat source, an oven heating method for heating the entire fixing portion with a heat source, and a hot plate heating system in which plates having a transferred material sandwiched therebetween are heated, a toner image being formed on said transferred material.
In the method using a halogen lamp as a heat source, it is widely known to the art to use a pair of rollers arranged to be capable of applying a predetermined pressure to the transferred material and the toner held therebetween. In this case, at least one of the rollers is formed hollow and a columnar halogen lamp is arranged within the inner space of the hollow roller. In the method of using a halogen lamp, a nip portion is formed between the hollow roller having the halogen lamp arranged therein and the other roller, i.e., a pressurizing roller, and these two rollers are rotated to permit the transferred material having a toner image formed thereon to be guided into the nip portion, with the result that pressure and heat are applied to the transferred material having a toner image formed thereon.
To be more specific, the transferred material, e.g., a paper sheet, having a toner image formed thereon is guided to the nip portion between the hollow heating roller having a halogen lamp arranged therein and the rotating pressurizing roller so as to melt the toner on the paper sheet and, thus, to fix the toner image to the paper sheet.
In the fixing apparatus using a halogen lamp, however, the light and the infrared rays are radiated from the halogen lamp in the entire circumferential direction of the heating roller so as to heat the entire heating roller. As a result, the heat conversion efficiency is 60 to 70% because of the loss in the conversion of the light into heat and the efficiency of warming the air within the heating roller and transmitting the heat to the heating roller, leading to a large power consumption. In addition, a long warming time is required.
Under the circumstances, an improved fixing apparatus has been proposed in recent years. Specifically, it is proposed that a thin heat resistant film movable in tight contact with a heating body is formed into an endless belt or a cylinder, and a material to be heated, which is in tight contact with the heat resistant film, is moved together with the film so as to permit the film to impart the heat energy of the heating body to the material to be heated. Incidentally, the heat resistant film has in general a width conforming with the maximum width of the transferred material. It follows that, in the fixing apparatus using the particular film, it is necessary to control the temperature to be uniform in the longitudinal direction of the heating body. As a result, the uniformity in the manufacturing step and the temperature control with a high accuracy in the operating step are required, leading to an increased manufacturing cost of the apparatus.
Incidentally, when it comes to a high speed copying machine capable of making a large number of copies per unit time, the heating time is shortened in general. As a result, it is necessary to use a heating body having a large heat capacity, leading to an increased power consumption. Also, the total power consumption is rendered unduly large so as to give rise to an inconvenience in terms of the safety standards.
In order to overcome the above-noted problems inherent in the heater fixation and the film fixation, a fixing apparatus using an induction heating is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 9-258586 and Japanese Patent Disclosure No. 8-76620.
Specifically, Japanese Patent Disclosure No. 9-258586 discloses a fixing apparatus, in which an electric current is allowed to flow through an induction coil prepared by winding a coil about a core arranged along the rotary shaft of the fixing roller made of a metal so as to generate an induction current in the roller and, thus, to permit the metal roller itself to generate heat.
On the other hand, Japanese Patent Disclosure No. 8-76620 discloses a fixing apparatus comprising a conductive film having a magnetic field generating means housed therein and a pressurizing roller that is in tight contact with the conductive film. In this prior art, heat is generated from the conductive film so as to permit the toner image formed on a transferred material, which is transferred through the clearance between the conductive film and the pressurizing roller, to be fixed to the transferred material.
In the fixing apparatus of the induction heating system described above, the heating coil acting as a magnetic field generating means is arranged inside the heating roller. In many cases, the gap between the heating coil and the heating roller is very small. Therefore, many examples are reported in which the surface of the heating coil is covered with an insulating material in order to prevent the heating roller from being brought into contact with the heating coil and, thus, to prevent the heating coil from being broken. Incidentally, Japanese Patent Disclosure No. 10-111610 discloses an example that the insulating material is thermally shrinkable so as to fix the heating coil. It is possible to prevent the breakage of the heating coil and a short circuit caused by the contact between the heating roller and the coil by covering the heating coil with an insulating material.
However, in a high speed machine having a large number of output recording material sheets per unit time, the heating roller is rotated at a high speed. Therefore, where the heating coil is covered with an insulating material as described above, it is necessary to increase the thickness of the insulating material layer so as to ensure safety. This implies that the heat capacity of the insulating material is increased. It should be noted in this connection that the fixing apparatus utilizing the induction heating is required to produce the merit that the warm up time is short. In the prior art, however, the heat of the infrared ray radiated from the heating roller when the heating roller is heated and released toward the insulating material and the heating coil is absorbed by the insulating material. It follows that the warm up time is increased with increase in the heat capacity of the insulating material.
An object of the present invention is to provide a fixing apparatus of an induction heating system capable of shortening the warm up time while allowing the insulating material layer interposed between the heating coil and the heating roller to have a thickness large enough to ensure high insulating properties.
Another object of the present invention is to provide a fixing apparatus of an induction heating system, in which the heat generated from the heating roller is released inside the heating roller so as to prevent the temperature elevation of the heating coil.
According to a first aspect of the present invention, there is provided a fixing apparatus, comprising: a first hollow cylindrical rotor rotatable in an optional direction; a second rotor brought into contact with a single point on the outer circumferential surface of the first rotor with a predetermined contact pressure so as to be rotated in accordance with rotation of the first roller, a nip portion into which a transferred material is supplied being formed in the contact portion between the first and second rotors; an induction heating apparatus arranged within the first rotor so as to impart a magnetic flux to the first rotor and, thus, to generate an eddy current within the first rotor, thereby generating heat; and a covering member having a predetermined color effective for reflecting the infrared ray radiated from the first rotor and arranged between the first rotor and the induction heating apparatus so as to prevent the first rotor from being brought into direct contact with the induction heating apparatus.
According to a second aspect of the present invention, there is provided a fixing apparatus, comprising: a first hollow cylindrical rotor rotatable in an optional direction; a second rotor brought into contact with a single point on the outer circumferential surface of the first rotor with a predetermined contact pressure so as to be rotated in accordance with rotation of the first roller, a nip portion into which a transferred material is supplied being formed in the contact portion between the first and second rotors; an induction heating apparatus arranged within the first rotor so as to impart a magnetic flux to the first rotor and, thus, to generate an eddy current within the first rotor, thereby generating heat; a first covering member having a predetermined color effective for reflecting the infrared ray and arranged in the free space between the first rotor and the induction heating apparatus so as to prevent the first rotor from being brought into direct contact with the induction heating apparatus; and a second covering member having a predetermined color effective for reflecting the infrared ray and arranged in the free space between the first covering member and the induction heating apparatus so as to prevent the first rotor from being brought into direct contact with the induction heating apparatus.
Further, according to a third aspect of the present invention, there is provided a fixing apparatus for an electrophotographic apparatus, in which an AC current is supplied to an electromagnetic induction coil arranged in close proximity to an endless member having a metal layer formed of a conductor so as to generate heat in the endless member for heating a transferred material to which a toner image is fixed, comprising:
a coil member support member for supporting the coil member of the induction heating apparatus; and
an adhesive layer for fixing the coil member to the coil member supporting member.